Galaxy Zoo Starburst Talk

BPT Diagram Results

  • trouille by trouille scientist, moderator, admin

    If you've just read Part 3 of the How-To-Guide and would like to participate in the follow-up discussion here, please do!

    Posted

  • jules by jules moderator

    Well - what a coincidence - I've been working on BPT plots for mergers for the last couple of days! FWIW here are my results:

    This is my dashboard but I think it's easier to see what's going on if I post the plots too.

    First those galaxies showing no signs of merging:

    Quench Sample - NOT merging

    Quench Sample NOT merging

    Quench Control - NOT merging

    Quench Control NOT merging

    And the mergers / tidal tails galaxies:

    Quench Sample - mergers

    Quench Sample - mergers

    Quench Control - mergers

    enter image description here

    I think this shows quite clearly that AGNs have a role to play in quenching star formation. Both Quench Sample plots show more galaxies in the AGN arm than appear in the corresponding Quench Control plots. This is particularly striking in the Sample mergers v Control mergers.

    Looking at the non-merging galaxies there is more of a "starburst spread" in the Control non-merging group.

    Both Sample and Control mergers show some star forming examples. Somehow I was expecting fewer in the Quench Sample. I'll think about that one...

    Also, there are more Quench Sample mergers (505) than Control mergers (245). No idea whether this is statistically significant. It seems to suggest mergers have a role to play in quenching star formation as well.

    I'm hoping the data is clean and complete enough by now for all this to make some sense! I haven't found anything new - just corroborated what is already in the literature.

    Bear in mind that 2 weeks ago I wasn't too sure what a BPT diagram was. 😮

    I'm now tempted to have a look at how morphology fits into the merger scenario. Not sure how much use that would be though. Or maybe take up astropixie's suggestions here.

    Or I might just go put the kettle on....

    Posted

  • trouille by trouille scientist, moderator, admin

    Great to see this response Jules. Yes, from those plots it really does seem to be that AGN activity might be part of what's causing the quenching.

    Has anyone tried splitting their BPT diagram to show the low mass post-quenched galaxies vs mid-mass post-quenched galaxies vs high-mass post-quenched galaxies (and the same for the control)? I wonder if there's a trend in mass, with more massive post-quenched galaxies more likely to need AGN activity to help them in the process? I was thinking about this after re-reading the Kaviraj article (I believe this is the 3rd one in the article summaries that MZevin provided).

    I've also been thinking about one of the lines you have in here --

    Also, there are more Quench Sample mergers (505) than Control mergers
    (245). No idea whether this is statistically significant. It seems to
    suggest mergers have a role to play in quenching star formation as
    well.

    Whoa. That's definitely statistically significant. If you take the square root of the total number of sources in each sample, you get a first estimate for the error on that value. In this case, you get: 505 +/- 22.5 (post-quench) and 245 +/- 15.65 (control). They're well outside each other's error bars.

    Let's run with this. What more can we learn if we look at different variables in the context of this difference in merger fraction between our post-quenched galaxies and control galaxies?

    Thanks for the inspiration for 'How-To-Guide' blog post #4! I'm off to write that up now and will check back in soon.

    Posted